In one of the several forwards to this book, the author comments that a book about writing should be short. Indeed, the essence of the book is 29 pages - weighty enough that aspiring writers should read it, often. Another 100 pages or so gives useful insights on applying that core material. The rest of the book, which lists for $8, is autobiography which (A) while interesting would be difficult to publish in its own right, and (B) bulks out the text so you don't feel slighted by $4.
King is indeed a skillful writer, making the reader feel very comfortable (save for copious obscenities) and expresses his advice clearly and usefully. Being successful and talented, his advice is valuable being from one who has lived the reality of the industry, providing subtle suggestions and contradictions which add value far beyond what an academic portrayal of the craft would usually entail.
Thinking of writing? Get this book. The slim portion on "Toolbox" is more than worth the cover price.